Known technologies related to the control of communication paths include MultiProtocol Label Switching-Traffic Engineering (MPLS-TE).
Referring to FIGS. 1A and 1B, a change of the communication path using MPLS-TE will be described. In changing the path using MPLS-TE, settings of a new path are previously made in each of relay apparatuses (e.g. routers) in an MPLS network, apart from settings of the old path. In FIG. 1A, upper tables illustrates settings of an old path, and lower tables illustrates settings of a new path, which are made apart from the settings of the old path. From a certain point in time on and after the settings were made, a relay apparatus serving as the entrance of the new path changes a label to be attached to a packet received from a client terminal, from an old label to a new label. In FIGS. 1A and 1B, a relay apparatus 1 changes a label to be attached to a packet, from “label 3” to “label 4”. Thus, each relay apparatus can transfer the packet along the new path using the corresponding lower table.
However, MPLS-TE is a technology for packet communication, and it is not assumed that MPLS-TE is applied to communications using the Hyper Text Transfer Protocol (HTTP) or the like. Accordingly, if the path of a request message and the path of a response message are required to be the same in communications using HTTP or the like, it is not appropriate to change the path by using a technology such as MPLS-TE as it is. This is because using a technology such as MPLS-TE as it is may cause a situation where while a request message is transferred along the old path, a response message is transferred along the new path.
There has been a technology by which plural relay apparatuses collaborate to calculate delay time for each priority and delay time for each path and to change the path on the basis of the delay time. However, the above-mentioned problem is not considered even in this conventional technology. The timing when the resources associated with the old path are deleted is not considered, either.
There is also a technology of previously setting a time limit to a path which will go out of use and deleting information on that path when the time limit expires. However, this technology has a problem that a failure to properly set a time limit would increase the time over which the relay apparatus manages both the resources associated with the old path and those associated with the new path and thus the load on the relay apparatus would be increased.
As seen, in changing the path in communications where the path of the request message and the path of the response message are required to be the same, sufficient consideration is not given to when the resources associated with the old path would be deleted.
In other words, the conventional technique cannot early release resources associated with the path before the change, when changing the path or route in the communication where the path or route of the request message and the path or route of the response message are required to be the same.